This invention relates to a method of manufacturing a ferromagnetic metal film type magnetic recording medium which has improved electro-magnetic conversion characteristics and high uniformity.
A conventional magnetic recording medium has been manufactured by a method in which magnetic powder, typically .gamma.-Fe.sub.2 O.sub.3, dispersed in organic binder is coated over a non-magnetic support and is then dried. Recently, in order to increase the recording density, a method of manufacturing a magnetic recording medium by forming a ferromagnetic metal film by vacuum deposition, sputtering or plating has been proposed, and an effort for practicing the method has been made.
The method of manufacturing a magnetic recording medium by vacuum deposition is especially advantageous in that, unlike the method of manufacturing a magnetic recording medium by plating, treatment of waste solution is unnecessary. Moreover, the manufacturing process is simple and the deposition speed is high. In order to improve the close contact of the vacuum-evaporated film with the base or to improve the electro-magnetic conversion characteristic, a method has been proposed in which a metal vapor flow from the evaporating source, namely, the crucible is ionized with high frequency power or thermions. The metal vapor flow thus ionized is applied to the base to form the film. This conventional method has been practically employed for certain purposes; however, it has not been suitable for the case where, as in the case of manufacturing a magnetic tape, an uniform film is formed on a web-shaped support for a long period of time.
In order to eliminate the above-described drawbacks and to improve the electro-magnetic conversion characteristic, the inventors have conducted intensive research on a method of forming a stable film by ionizing a metal vapor flow with high frequency power, and have achieved the present invention.